Vertical fin field effect transistor with air gap spacers

ABSTRACT

A fin field effect transistor device with air gaps, including a source/drain layer on a substrate, one or more vertical fin(s) in contact with source/drain layer, a gate metal fill that forms a portion of a gate structure on each of the one or more vertical fin(s), and a bottom void space between the source/drain layer and the gate metal fill.

BACKGROUND Technical Field

The present invention generally relates to formation of air gaps betweenfield effect transistor (FET) gates and source/drain regions, and moreparticularly to the fabrication and removal of sacrificial spacers toform air channels in the FET structure.

Description of the Related Art

A Field Effect Transistor (FET) typically has a source, a channel, and adrain, where current flows from the source to the drain, and a gate thatcontrols the flow of current through the channel. Field EffectTransistors (FETs) can have a variety of different structures, forexample, FETs have been fabricated with the source, channel, and drainformed in the substrate material itself, where the current flowshorizontally (i.e., in the plane of the substrate), and finFETs havebeen formed with the channel extending outward from the substrate, butwhere the current also flows horizontally from a source to a drain. Thechannel for the finFET can be an upright slab of thin rectangular Si,commonly referred to as the fin with a gate on the fin, as compared to aMOSFET with a single gate in the plane of the substrate. Depending onthe doping of the source and drain, an n-FET or a p-FET may be formed.

Examples of FETs can include a metal-oxide-semiconductor field effecttransistor (MOSFET) and an insulated-gate field-effect transistor(IGFET). Two FETs also may be coupled to form a complementary metaloxide semiconductor (CMOS), where a p-channel MOSFET and n-channelMOSFET are coupled together.

With ever decreasing device dimensions, forming the individualcomponents and electrical contacts becomes more difficult. An approachis therefore needed that retains the positive aspects of traditional FETstructures, while overcoming the scaling issues created by formingsmaller device components.

SUMMARY

In accordance with an embodiment of the present invention, a fin fieldeffect transistor (finFET) device with air gaps is provided. Thearrangement of the fin field effect transistor device includes asource/drain layer on a substrate. The arrangement further includes oneor more vertical fin(s) in contact with source/drain layer. Thearrangement further includes a gate metal fill that forms a portion of agate structure on each of the one or more vertical fin(s), and a bottomvoid space between the source/drain layer and the gate metal fill.

In accordance with another embodiment of the present invention, a methodis provided for forming a fin field effect transistor device with airgaps. The method includes the step of forming one or more vertical finson a substrate. The method further includes the step of forming asource/drain layer on the substrate in contact with the one or morevertical fins on a substrate. The method further includes the step offorming a sacrificial bottom spacer on the source/drain layer. Themethod further includes the step of forming a sacrificial spacer cap onthe sacrificial bottom spacer. The method further includes the step ofremoving the sacrificial bottom spacer to form a bottom void spacebetween the source/drain layer and the sacrificial spacer cap.

In accordance with yet another embodiment of the present invention, afin field effect transistor device with air gaps is provided. Thearrangement of the fin field effect transistor device includes asource/drain layer on a substrate. The arrangement further includes avertical fin in contact with source/drain layer. The arrangement furtherincludes a gate structure that covers a portion of the vertical fin. Thearrangement further includes a top source/drain on the vertical fin, andan upper void space between the top source/drain and the gate structure.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional side view of a sidewall image transfer layerstack on a semiconductor-on-insulator substrate, in accordance with anembodiment of the present invention;

FIG. 2 is a cross-sectional side view of a plurality of sidewall spacerson the sidewalls of the sacrificial mandrels and on the fin templatelayer, in accordance with an embodiment of the present invention;

FIG. 3 is a cross-sectional side view of a fin template and templateliner on each of a plurality of vertical fins formed on a BOX layer, inaccordance with an embodiment of the present invention;

FIG. 4 is a cross-sectional side view of an inner protective cap and anouter protective cap on each vertical fin, in accordance with anembodiment of the present invention;

FIG. 5 is a cross-sectional side view of a provisional layer on theexposed lateral surfaces of the substrate, and dummy sidewalls on theouter protective cap, in accordance with an embodiment of the presentinvention;

FIG. 6 is a cross-sectional side view of an exposed lower portion of theouter protective caps after removal of the provisional layer, inaccordance with an embodiment of the present invention;

FIG. 7 is a cross-sectional side view of a top portion of the protectivecaps removed from fin templates between the dummy sidewalls, inaccordance with an embodiment of the present invention;

FIG. 8 is a cross-sectional side view of the outer protective cap andinner protective cap on the sidewalls of the fin template, templateliner, and vertical fin, after removal of the dummy sidewalls, inaccordance with an embodiment of the present invention;

FIG. 9 is a cross-sectional side view of a source/drain layer formed onthe exposed portion of the vertical fins and BOX layer, in accordancewith an embodiment of the present invention;

FIG. 10 is a cross-sectional side view of dopant diffusion into a lowerportion of the vertical fins utilizing a heat treatment, in accordancewith an embodiment of the present invention;

FIG. 11 is a cross-sectional side view of a bottom spacer cap on thesacrificial bottom spacer, in accordance with an embodiment of thepresent invention;

FIG. 12 is a cross-sectional side view of a sacrificial spacer cap onthe sacrificial bottom spacer, and a dummy gate fill on the sacrificialspacer cap, in accordance with an embodiment of the present invention;

FIG. 13 is a cross-sectional side view of an upper spacer liner on anupper portion of the inner protective cap, in accordance with anembodiment of the present invention;

FIG. 14 is a cross-sectional side view of an upper spacer liner on anupper portion of the inner protective cap after removal of the dummygate fill, in accordance with an embodiment of the present invention;

FIG. 15 is a cross-sectional side view of a protective cover layer andgate dielectric layer on the upper spacer liner and vertical fin, inaccordance with an embodiment of the present invention;

FIG. 16 is a cross-sectional side view of a temporary fill layer fillingthe spaces between the protective cover layer on the vertical fins, inaccordance with an embodiment of the present invention;

FIG. 17 is a cross-sectional side view of a partially removed temporaryfill layer exposing a portion of the protective cover layer, inaccordance with an embodiment of the present invention;

FIG. 18 is a cross-sectional side view of an exposed upper spacer linerafter removal of a portion of the gate dielectric layer and protectivecover layer, in accordance with an embodiment of the present invention;

FIG. 19 is a cross-sectional side view of an exposed protective coverlayer after removal of the temporary fill layer, in accordance with anembodiment of the present invention;

FIG. 20 is a cross-sectional side view of a work function layer on theupper spacer liner and gate dielectric layer, in accordance with anembodiment of the present invention;

FIG. 21 is a cross-sectional side view of a gate metal fill on the workfunction layer, in accordance with an embodiment of the presentinvention;

FIG. 22 is a cross-sectional side view of a reduced height gate metalfill on the work function layer, in accordance with an embodiment of thepresent invention;

FIG. 23 is a cross-sectional side view of a recessed gate metal fill,work function layer, gate dielectric layer, and sacrificial spacer cap,in accordance with an embodiment of the present invention;

FIG. 24 is a cross-sectional side view of an inner liner on a recessedgate metal fill, work function layer, gate dielectric layer, andsacrificial spacer cap, in accordance with an embodiment of the presentinvention;

FIG. 25 is a cross-sectional side view of a sacrificial top spacer fillon the inner liner over the vertical fins and gate structures, inaccordance with an embodiment of the present invention;

FIG. 26 is a cross-sectional side view of a reduced height sacrificialtop spacer fill on the inner liner after partial removal, in accordancewith an embodiment of the present invention;

FIG. 27 is a cross-sectional side view of a top source/drain region onthe top surfaces of the vertical fins and sacrificial top spacer fill,in accordance with an embodiment of the present invention;

FIG. 28 is a cross-sectional side view of dopant diffusion into an upperportion of the vertical fins utilizing a heat treatment, in accordancewith an embodiment of the present invention;

FIG. 29 is a cross-sectional side view of a top source/drain on thevertical fins after removal of the exposed portion of the sacrificialtop spacer fill, in accordance with an embodiment of the presentinvention;

FIG. 30 is a top view of a fin layout showing hidden features, inaccordance with an embodiment of the present invention;

FIG. 31 is a cross-sectional side view of an interlayer dielectric layeron the top source/drain and previously exposed inner liner, inaccordance with an embodiment of the present invention;

FIG. 32 is a cross-sectional top view of FIG. 31 along the AA sectionshowing a plurality of vertical fins and intervening sacrificial topspacer fill in the U-shaped troughs with an opening in the ILD layer, inaccordance with an embodiment of the present invention;

FIG. 33 is a cross-sectional side view of upper void spaces formed inthe U-shaped troughs after removal of the sacrificial top spacer fill,in accordance with an embodiment of the present invention;

FIG. 34 is a cross-sectional top view of FIG. 33 along the same AAsection as FIG. 31 showing a plurality of vertical fins and upper voidspaces in the U-shaped troughs, in accordance with an embodiment of thepresent invention;

FIG. 35 is a cross-sectional side view of bottom void spaces formed inthe U-shaped sacrificial spacer caps after removal of the sacrificialbottom spacer, in accordance with an embodiment of the presentinvention;

FIG. 36 is a cross-sectional side view of enlarged bottom void spacesformed between the gate dielectric layer and source/drain layer afterremoval of the sacrificial spacer cap, in accordance with an embodimentof the present invention;

FIG. 37 is a cross-sectional side view of further enlarged bottom voidspaces formed by partial removal of the source/drain layer, inaccordance with an embodiment of the present invention;

FIG. 38 is a cross-sectional side view of a silicide layer formed on thefaceted sides of the source/drain layer, and an opening in the ILDlayer, in accordance with an embodiment of the present invention;

FIG. 39 is a cross-sectional side view of a silicide layer formed on thetop source/drain layer, in accordance with an embodiment of the presentinvention;

FIG. 40 is a cross-sectional side view of an ILD refill formed in theopening above the top source/drain, in accordance with an embodiment ofthe present invention;

FIG. 41 is a cross-sectional side view of a second opening formed in theILD layer above the top source/drain layer, in accordance with anembodiment of the present invention;

FIG. 42 is a cross-sectional side view of a conductive electricalcontact formed in the second opening formed in the ILD layer to thesilicide layer, in accordance with an embodiment of the presentinvention; and

FIG. 43 is a top view of a multi-fin device showing the electricalcontacts to the various device components, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

Principles and embodiments of the present invention relate generally toformation of sacrificial spacers within a fin field effect transistor(finFET) device structure that can be subsequently removed to form airgaps between the source/drains and gate structure. The air gaps canprovide reduced parasitic outer fringe capacitance and/or a higherbreakdown voltage between a gate and adjacent source/drain regions.Power consumption also can be reduced by reducing leakage currents.

Principles and embodiments of the present invention also relategenerally to forming a sacrificial bottom spacer below a gate structureand a sacrificial top spacer above the gate structure, where thesacrificial top spacer and sacrificial bottom spacer can be at leastpartially laterally etched to form a void space adjacent to the gatestructure. The sacrificial bottom spacer and sacrificial top spacer canbe removed after overlying layers and/or components have been formedthat would prevent subsequent layers from filling in the air gap if thesacrificial bottom spacer or sacrificial top spacer had been removed.

Principles and embodiments of the present invention also relategenerally to forming a merged top source/drain to cap an upper voidspace and/or a bi-layer bottom source/drain in forming a bottom voidspace. A bottom void space can be further increased in size utilizing acrystallographically selective etch of the bottom source/drain.

Exemplary applications/uses to which the present principles can beapplied include, but are not limited to: formation of complementarymetal oxide silicon (CMOS) field effect transistors (FETs) formed bycoupled finFETs, digital gate devices (e.g., NAND, NOR, XOR, etc.), andmemory devices (e.g., SRAM, DRAM, etc.).

In various embodiments, the materials and layers can be deposited byphysical vapor deposition (PVD), chemical vapor deposition (CVD), atomiclayer deposition (ALD), molecular beam epitaxy (MBE), or any of thevarious modifications thereof, for example, plasma-enhanced chemicalvapor deposition (PECVD), metal-organic chemical vapor deposition(MOCVD), low pressure chemical vapor deposition (LPCVD), electron-beamphysical vapor deposition (EB-PVD), and plasma-enhanced atomic layerdeposition (PEALD). The depositions can be epitaxial processes, and thedeposited material can be crystalline. In various embodiments, formationof a layer may be by one or more deposition processes, where, forexample, a conformal layer can be formed by a first process (e.g., ALD,PEALD, etc.) and a fill can be formed by a second process (e.g., CVD,electrodeposition, PVD, etc.).

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps may be varied within the scope of the present invention.

It should be noted that certain features may not be shown in all figuresfor the sake of clarity. This is not intended to be interpreted as alimitation of any particular embodiment, or illustration, or scope ofthe claims.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a cross-sectional side viewof a sidewall image transfer layer stack on a semiconductor-on-insulatorsubstrate is shown in accordance with an embodiment of the presentinvention.

In one or more embodiments, a substrate 110 can be a semiconductor or aninsulator with an active surface semiconductor layer. The substrate canbe crystalline, semi-crystalline, microcrystalline, or amorphous. Thesubstrate can be essentially (i.e., except for contaminants) a singleelement (e.g., silicon), primarily (i.e., with doping) of a singleelement, for example, silicon (Si) or germanium (Ge), or the substratecan include a compound, for example, Al₂O₃, SiO₂, GaAs, SiC, or SiGe.The substrate can also have multiple material layers, for example, asemiconductor-on-insulator substrate (SeOI), a silicon-on-insulatorsubstrate (SOI), germanium-on-insulator substrate (GeOI), orsilicon-germanium-on-insulator substrate (SGOI). The substrate can alsohave other layers forming the substrate, including high-k oxides and/ornitrides. In one or more embodiments, the substrate 110 can be a siliconwafer. In various embodiments, the substrate may be a single crystalsilicon (Si), silicon germanium (SiGe), or III-V semiconductor (e.g.,GaAs) wafer, or have a single crystal silicon (Si), silicon germanium(SiGe), or III-V semiconductor (e.g., GaAs) surface/active layer. Thesurface/active layer can be on a buried oxide (BOX) layer that canphysically separate and electrically insulate the active layer from amechanically supporting portion of the substrate 110.

In one or more embodiments, a buried oxide layer 120 can be formed on atleast a portion of a substrate 110. An active semiconductor layer (ASL)130 can be on the BOX layer 120. A fin template liner 140 can be formedon at least a portion of the active semiconductor layer 130, and a fintemplate layer 150 can be formed on the fin template liner 140, wherethe fin template layer and fin template liner can be hardmask layers. Amandrel layer 160 can be formed on the fin template layer 150, and amandrel template layer 170 can be formed on the mandrel layer 160, wherethe mandrel template layer 170 can be a hardmask layer.

In one or more embodiments, one or more vertical fin(s) can be formed onthe BOX layer 120 by a sidewall image transfer process, where anarrangement of sidewall spacers formed on one or more sacrificialmandrels can be transferred to an active semiconductor layer 130.

In various embodiments, a fin template layer 150 can be a hard masklayer for masking the substrate during transfer of a vertical finpattern to the active semiconductor layer 130. The fin template layer150 can be a silicon oxide (SiO), a silicon nitride (SiN), a siliconoxynitride (SiON), a silicon carbonitride (SiCN), a silicon boronitride(SiBN), a silicon borocarbide (SiBC), a silicon boro carbonitride(SiBCN), a boron carbide (BC), a boron nitride (BN), a titanium nitride(TiN) or combinations thereof, where the fin template layer 150 mayinclude one or more layers. The fin template layer 120 can also act asan etch-stop layer for forming sacrificial mandrels from a mandrel layer160.

In one or more embodiments, a fin template liner 140 can be formedbetween the active semiconductor layer 130 and the fin template layer150, where the fin template liner 140 can protect the activesemiconductor layer 130 from the introduction of defects duringformation of the fin template layer 150. In various embodiments, the fintemplate liner 140 can be a silicon oxide (SiO), a silicon oxynitride(SiON), or a combination thereof.

In various embodiments, mandrel layer 160 can be a sacrificial materialthat can be easily and selectively patterned and etched. The mandrellayer 160 can be amorphous silicon (a-Si), poly-silicon (p-Si),amorphous carbon (a-C), silicon-germanium (SiGe), or suitablecombinations thereof.

In one or more embodiments, a mandrel template layer 170 can be formedon the mandrel layer 160, where the mandrel template layer 170 can be ahard mask layer. The mandrel template layer 170 can be a silicon oxide(SiO), a silicon nitride (SiN), a silicon oxynitride (SiON), a siliconcarbonitride (SiCN), a silicon boronitride (SiBN), a silicon borocarbide(SiBC), a silicon boro carbonitride (SiBCN), a boron carbide (BC), aboron nitride (BN), a titanium nitride (TiN) or combinations thereof,where the mandrel template layer 170 may include one or more layers.

In one or more embodiments, a mandrel mask layer 175 can be formed onthe mandrel template layer 170, where the mandrel mask layer 175 can bea lithographic resist material (e.g., a photo resist material, an e-beamresist material, etc.) that can be patterned and developed to exposeportions of the underlying mandrel template layer 170.

In one or more embodiments, the mandrel mask layer 175 can be a positiveor negative resist material, for example, Poly (methyl methacrylate)(PMMA) or SU-8, or an electron-beam cured material, for example,hydrogen silsesquioxane (HSQ).

In various embodiments, a mandrel pattern can be formed in the mandrelmask layer 175 and transferred to the mandrel template layer 170 andmandrel layer 160 to form one or more sacrificial mandrels on the fintemplate layer 150.

In various embodiments, a plurality of vertical fins can be formed by asidewall image transfer (SIT) process, where the SIT process can be aself-aligned double patterning (SADP), or self-aligned quadruplepatterning (SAQP) that repeats SADP to provide quadruple features at atighter pitch between vertical fins. In various embodiments, a directprint can be used to provide fins with a looser pitch.

FIG. 2 is a cross-sectional side view of a plurality of sidewall spacerson the sidewalls of the sacrificial mandrels and on the fin templatelayer, in accordance with an embodiment of the present invention.

In one or more embodiments, one or more mandrel template(s) 171 can beformed on the mandrel layer 160, and one or more sacrificial mandrels161 can be formed on the fin template layer 150. In various embodiments,the sacrificial mandrels 161 can be formed by removing portions of themandrel layer 160 exposed between mandrel template(s) 171, whereportions of the mandrel layer 160 can be removed, for example, by adirectional dry plasma etching process (e.g., a reactive ion etch(RIE)).

In one or more embodiments, sidewall spacers 181 can be formed on theone or more sacrificial mandrels, where the sidewall spacers 181 can beformed by blanket depositing a selectively etchable material on theexposed fin template layer surface, sacrificial mandrel sidewalls, andtop surface of the mandrel template(s) 171, and then etch back theblanket deposited materials to leave the sidewall spacers 181.

In various embodiments, the sidewall spacers 181 can be formed ofsilicon oxide (SiO), silicon nitride (SiN), silicon oxynitride (SiON),or combinations thereof, where the sidewall spacers 181 can beselectively etchable in relation to the mandrel template(s) 171,sacrificial mandrels 161, fin template layer 150, fin template liner140, and active semiconductor layer 130.

FIG. 3 is a cross-sectional side view of a fin template and templateliner on each of a plurality of vertical fins formed on a BOX layer, inaccordance with an embodiment of the present invention.

In one or more embodiments, the pattern of the sidewall spacers 181 canbe transferred to the underlying fin template liner 140 and/or fintemplate layer 150 to form a template liner 141 and/or fin template 151on each of a plurality of vertical fins 131. The template liner 141and/or fin template 151 can have a width and length that can determinethe lateral size (i.e., width and length) of a formed vertical fin 131.

In one or more embodiments, the active semiconductor layer (ASL) 130 canbe removed from between the template liners 141 and/or fin templates 151down to the BOX layer 120, such that the thickness of the activesemiconductor layer 130 can define the height of the one or morevertical fin(s) being formed. In various embodiments, the activesemiconductor layer 130 may not be removed all the way down to the BOXlayer, so the etching depth can determine the height of the one or morevertical fin(s) being formed.

In one or more embodiments, the one or more vertical fin(s) 131 can beformed by a directional, dry plasma etch that removes a portion of theexposed active semiconductor layer 130 from between the template liner141 and/or fin template 151, where the dry plasma etch can be an RIE.

FIG. 4 is a cross-sectional side view of an inner protective cap and anouter protective cap on each vertical fin, in accordance with anembodiment of the present invention.

In one or more embodiments, a protective cap, that can include an innerprotective cap 190 and an outer protective cap 200, can be formed oneach vertical fin 131, template liner 141 and/or fin template 151. Theprotective cap can be formed by depositing an inner protective layer andan outer protective layer on the exposes surfaces of the vertical fin(s)131, template liner 141 and/or fin template 151, and underlying activesemiconductor layer 130 or BOX layer 120, depending on the depth of etchused to remove material from the active semiconductor layer (ASL) 130 toform the vertical fin(s) 131 (herein referred to as the BOX layer/ASL).At least a portion of an inner protective layer and/or the outerprotective layer can be removed from the exposed surface of the activesemiconductor layer 130 or the BOX layer 120 by a directional etch(e.g., RIE) to leave the inner protective cap(s) 190 and outerprotective cap(s) 200 on the vertical fin(s) 131, template liner(s) 141and/or fin template(s) 151.

In one or more embodiments, the inner protective liner 190 can be adifferent material from the outer protective liner 200, where the outerprotective liner 200 can be selectively etchable versus the innerprotective liner 190. In various embodiments, the inner protective liner190 can be formed of silicon oxide (SiO), silicon nitride (SiN), orsilicon oxynitride (SiON). In various embodiments, the outer protectiveliner 200 can be formed of silicon oxide (SiO), silicon nitride (SiN),or silicon oxynitride (SiON).

In one or more embodiments, the inner protective liner 190 can beconformally deposited on the exposed surfaces of the vertical fin(s)131, template liner 141 and/or fin template 151, for example by ALD,PEALD, CVD, PECVD, or combinations thereof.

In one or more embodiments, the inner protective liner 190 can have athickness in the range of about 1 nm to about 10 nm, or in the range ofabout 2 nm to about 4 nm. In various embodiments, the thickness of theconformally deposited inner protective liner 190 can be controlled bythe deposition process parameters.

In one or more embodiments, the outer protective liner 200 can beconformally deposited on the exposed surfaces of the inner protectiveliner 190, for example by ALD, PEALD, CVD, PECVD, or combinationsthereof.

In one or more embodiments, the outer protective liner 200 can have athickness in the range of about 1 nm to about 10 nm, or in the range ofabout 2 nm to about 4 nm. In various embodiments, the thickness of theconformally deposited outer protective liner 200 can be controlled bythe deposition process parameters.

FIG. 5 is a cross-sectional side view of a provisional layer on theexposed lateral surfaces of the substrate, and dummy sidewalls on theouter protective cap, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a provisional layer 210 can be formed on atleast a portion of the exposed lateral surfaces of the BOX layer/ASL andat least a portion of the outer protective cap 200, where theprovisional layer 210 can be formed on the BOX layer/ASL by adirectional deposition, for example, PVD or a gas cluster ion beam(GCIB) process. In one or more embodiments, the provisional layer 210can be formed by CVD or PECVD, where the provisional layer 210 can beblanket deposited on the outer protective cap 200, and at least aportion of the exposed surfaces of the BOX layer 120. Theblanket-deposited provisional layer 210 can extend above the topsurfaces of the protective cap, wherein chemical-mechanical polishing(CMP) can be used to remove a portion of the provisional layer andprovide a planarized surface. A selective etchback process, for example,by RIE, can be used to reduce the height of the provisional layer 210,where the provisional layer can then cover a lower portion of the outerprotective cap 200. In various embodiments, the covered lower portioncan be equal to or less than a third of the height of the vertical fin131, or in the range of a quarter to a third of the height of thevertical fin 131.

In one or more embodiments, the provisional layer 210 can be amorphoussilicon (a-Si) or polycrystalline silicon (p-Si), or a combinationthereof, where the provisional layer 210 can be selectively removed frombetween the outer protective cap(s) 200.

In one or more embodiments, the provisional layer 210 can have athickness in the range of about 5 nm to about 100 nm, or in the range ofabout 10 nm to about 50 nm, or in the range of about 20 nm to about 30nm, where the thickness of the provisional layer 210 can define thethickness of a subsequently formed bottom source/drain layer.

In one or more embodiments, a dummy sidewall 220 can be formed on atleast a portion of the outer protective cap 200 on each vertical fin131, where the dummy sidewall can extend from the top of the outerprotective cap to the surface of the provisional layer to cover apredetermined length of the outer protective cap 200 on the verticalfin(s) 131. The dummy sidewall 220 can protect at least a portion of theouter protective cap 200 during removal of the provisional layer.

In one or more embodiments, the dummy sidewall 220 can be a metal oxide,where the metal oxide can be a high-k metal oxide, for example, hafniumoxide (HfO), lanthanum oxide (e.g., La₂O₃), lanthanum aluminum oxide(e.g., LaAlO₃), zirconium oxide (e.g., ZrO₂), zirconium silicon oxide(e.g., ZrSiO₄), tantalum oxide (e.g., TaO₂, Ta₂O₅), titanium oxide(e.g., TiO₂), yttrium oxide (e.g., Y₂O₃), or aluminum oxide (e.g.,Al₂O₃). The high-k metal oxide can further include dopants such aslanthanum and/or aluminum. The stoichiometry of the high-K compounds canvary.

In one or more embodiments, the dummy sidewall 220 can be formed byconformal deposition on the outer protective cap 200 and exposed surfaceof the provisional layer 210, and etching back the deposited materialfrom the top surface of the outer protective cap 200 and exposed surfaceof the provisional layer 210. The dummy sidewalls 220 can remain on thesidewalls of the outer protective cap 200, where the dummy sidewalls canwrap around the vertical fins 131. In various embodiments, the dummysidewalls can be conformally deposited by ALD, PEALD, CVD, PECVD, orcombinations thereof.

FIG. 6 is a cross-sectional side view of an exposed lower portion of theouter protective caps after removal of the provisional layer, inaccordance with an embodiment of the present invention.

In one or more embodiments, the provisional layer 210 can be removedfrom the BOX layer/ASL to expose the BOX layer/ASL and at least a lowerportion of the outer protective cap 200 along a height of vertical fin131 between the surface of the BOX layer/ASL and a bottom edge of thedummy sidewall 220. The provisional layer 210 can be removed by anisotropic etch, for example a wet etch or a gaseous etch, where theisotropic etch can be selective to the material of the provisionallayer.

FIG. 7 is a cross-sectional side view of a top portion of the protectivecaps removed from fin templates between the dummy sidewalls, inaccordance with an embodiment of the present invention.

In one or more embodiments, the outer protective cap 200 and the innerprotective cap 190 can be removed from the fin template 151 on the topof the vertical fin(s) 131, where the outer protective cap 200 and theinner protective cap 190 can be removed by a selective isotropic etch,while the dummy sidewalls 220 remain.

In one or more embodiments, the outer protective cap 200 and the innerprotective cap 190 can be removed from the lower portion of the verticalfin(s) 131 exposed by the removal of the provisional layer 210. Thelower portions of the outer protective cap 200 and the inner protectivecap 190 can be removed by the same selective isotropic etching used toremove the outer protective cap 200 and the inner protective cap 190 onthe top of the fin template 151. In various embodiments, the outerprotective cap 200 can be removed by a first etch selective to thematerial of the outer protective cap, and the inner protective cap 190can be removed by a second etch selective to the material of the innerprotective cap.

In various embodiments, the portion of the outer protective cap 200 andthe inner protective cap 190 on the sidewalls of the fin template 151,template liner 141, and vertical fin 131 remain where the outerprotective cap 200 is covered by the dummy sidewall 220. A lower portionof the vertical fin(s) 131 can be exposed after removal of the lowerportion of both the outer protective cap 200 and the inner protectivecap 190, where the height of the vertical fin(s) 131 exposed can bedetermined by the thickness of the provisional layer 210, which can bepredetermined based on the thickness of an intended bottom source/drainlayer.

FIG. 8 is a cross-sectional side view of the outer protective cap andinner protective cap on the sidewalls of the fin template, templateliner, and vertical fin, after removal of the dummy sidewalls, inaccordance with an embodiment of the present invention.

In one or more embodiments, the dummy sidewalls 220 can be removed fromthe outer protective liner 200, where the dummy sidewalls 220 can beselectively etched using an isotropic etch, for example, a wet etch. Theouter protective liner 200 can be exposed after removal of the dummysidewall 200.

In one or more embodiments, the width of an exposed lower portion of thevertical fin(s) 131 can be reduced, where the width can be reduced by aselective etching of the exposed vertical fin material. In variousembodiments, the etch can be an isotropic plasma etch, or an isotropicwet etch. Removal of at least a portion of the exposed portion of thevertical fin(s) 131 proximal to the BOX layer/ASL can provide forformation of a source/drain region that is partially embedded into thefin, which can require less subsequent diffusion of dopants from thesource/drain regions into the vertical fin to form intended junctions.

FIG. 9 is a cross-sectional side view of a source/drain layer formed onthe exposed portion of the vertical fins and BOX layer, in accordancewith an embodiment of the present invention.

In one or more embodiments, a source/drain layer 230 can be formed onthe BOX layer/ASL, where the source/drain layer 230 can form a bottomsource/drain for the device and provide dopant(s) to at least a lowerportion of the vertical fin(s) 131 adjacent to the source/drain layer230. In various embodiments, the doped lower portion of one or morevertical fin(s) 131 and the source/drain layer 230 can form a bottomsource/drain. The source/drain layer 230 can be in contact with one ormore vertical fin(s), where the source/drain layer can electricallycouple at least two adjacent vertical fins together to form a multi-finfinFET device.

In various embodiments, the source/drain layer 230 can be formed byepitaxial growth from the exposed surfaces of a crystalline vertical fin131, where the source/drain layer 230 can grow laterally from theexposed crystalline surface over the underlying BOX layer/ASL. Invarious embodiments, the BOX layer 120 may not influence the epitaxialgrowth of the source/drain layer 230, where the BOX layer 120 isamorphous. In various embodiments, an underlying ASL can provide acrystalline surface that also promotes the epitaxial growth of thesource/drain layer 230.

In various embodiments, the source/drain layer 230 may be the samematerial as the vertical fin(s) 131. The source/drain layer 230 can bedoped in-situ to have a predetermined concentration of dopant, where aportion of the dopant can subsequently migrate into at least a lowerportion of the vertical fin(s) 131 during a heat treatment. In variousembodiments, the source/drain layer 230 can be epitaxially grown, andthe height of the source/drain layer 230 can be subsequently reduced bya directional etch (e.g., RIE) to achieve an intended height.

In one or more embodiments, a sacrificial bottom spacer 240 can beformed on the source/drain layer 230, where the sacrificial bottomspacer 240 can be epitaxially grown on the source/drain layer 230. Thesacrificial bottom spacer 240 can be a material different from thesource/drain layer 230. In various embodiments, the sacrificial bottomspacer 240 can be silicon-germanium (Si_(x)Ge_(1-x)), where theSi_(x)Ge_(1-x) can have a high Ge concentration (e.g., >50%) to allowselective etching in relation to a silicon or low-Ge concentrationSi_(x)Ge_(1-x) source/drain layer 230. In various embodiments, thesacrificial bottom spacer 240 can be silicon-germanium (Si_(x)Ge_(1-x)),silicon oxide (SiO), silicon oxycarbide (SiOC), silicon oxycarbonitride(SiOCN), amorphous carbon (a-C), or suitable combinations thereof, thatcan be selectively etched in relation to the source/drain layer 230.

FIG. 10 is a cross-sectional side view of dopant diffusion into a lowerportion of the vertical fins utilizing a heat treatment, in accordancewith an embodiment of the present invention.

In one or more embodiments, the vertical fin(s) 131 and source/drainlayer 230 can be heated to facilitate diffusion of dopant from thesource/drain layer 230 into the adjacent vertical fin(s) 131, where thedopant can diffuse into a portion of the vertical fin in contact withthe source/drain layer 230. In various embodiments, the source/drainlayer 230 and vertical fin(s) 131 can be heat treated at a temperaturein the range of about 700° C. to about 1300° C., or in the range ofabout 900° C. to about 1100° C., where the heat treatment can be afurnace anneal, a rapid thermal anneal, or a laser anneal. In variousembodiments the anneal can be for a duration in the range of about 5seconds to about 1 hour, where the duration of the heat treatment candepend on the temperature.

In various embodiments, the source/drain layer 230 can have a dopantconcentration in the range of about 1×10¹⁹ to about 1×10²¹, or in therange of about 5×10¹⁹ to about 5×10²⁰. The bottom diffusion region 135in the lower portion of the vertical fin(s) 131 can have a dopantconcentration in the range of about 1×10¹⁸ to about 1×10²⁰, or in therange of about 5×10¹⁸ to about 5×10¹⁹, after the heat treatment.

FIG. 11 is a cross-sectional side view of a bottom spacer cap on thesacrificial bottom spacer, in accordance with an embodiment of thepresent invention.

In one or more embodiments, spacer cap layer 250 can be formed on thesacrificial bottom spacer 240, where the spacer cap layer 250 can be thesame material as the outer protective cap 200. In various embodiments,the thickness of the spacer cap layer 250 can be greater than thethickness of the outer protective cap 200.

FIG. 12 is a cross-sectional side view of a sacrificial spacer cap onthe sacrificial bottom spacer, and a dummy gate fill on the sacrificialspacer cap, in accordance with an embodiment of the present invention.

In one or more embodiments, the spacer cap layer 250 can be etched backto form a sacrificial spacer cap 255, where the etch-back can use anisotropic etch that also etches the outer protective cap 200. In variousembodiments, the portion of the outer protective cap 200 exposed abovethe surface of the spacer cap layer 250 can be removed, and thethickness of the spacer cap layer 250 can be reduced to form thesacrificial spacer cap 255.

In one or more embodiments, a dummy gate fill 260 can be formed on thesacrificial spacer cap 255, where the dummy gate fill 260 can beamorphous silicon (a-Si). The thickness of the dummy gate fill 260 candefine the length of a subsequently formed gate structure on thevertical fin 131, where the dummy gate fill may be aligned with a middleportion of the vertical fin.

In one or more embodiments, the dummy gate fill 260 can be blanketdeposited on the exposed surface of the sacrificial spacer cap(s) 255and inner protective cap 190 covering the vertical fin(s) 131 and fintemplate(s) 151. The blanket deposited dummy gate fill 260 can extendabove the top surfaces of the fin template(s) 151, and a chemicalmechanical polishing (CMP) can be used to remove excess material andreduce the height of the dummy gate fill 260 to the top surfaces of thefin template(s) 151. The CMP can provide a smooth, flat surface forsubsequent processing. The height of the dummy gate fill 260 can befurther reduced by a directional dry plasma etch, where the top surfaceof the dummy gate fill 260 can be reduced to a predetermined location onthe vertical fin 131 to define the gate length on a device channelformed by the vertical fin 131.

In one or more embodiments, the thickness of the reduced height dummygate fill 260 can be in the range of about 5 nm to about 40 nm, or inthe range of about 10 nm to about 20 nm, although other thicknesses arecontemplated.

FIG. 13 is a cross-sectional side view of an upper spacer liner on anupper portion of the inner protective cap, in accordance with anembodiment of the present invention.

In one or more embodiments, an upper spacer liner 270 can be formed onan exposed portion of the inner protective cap 190 above the dummy gatefill 260. The upper spacer liner 270 can be conformally deposited on atleast a portion of the exposed surface of the dummy gate fill 260, innerprotective cap 190, and top surface of the fin template 151, where theupper spacer liner 270 can be conformally deposited by ALD, PEALD, CVD,PECVD, or combinations thereof.

In one or more embodiments, the upper spacer liner 270 can be siliconoxide (SiO), silicon nitride (SiN), silicon oxynitride (SiON), orcombinations thereof, where the upper spacer liner 270 can beselectively etchable in relation to the dummy gate fill 260 and innerprotective cap 190.

A portion of the upper spacer liner 270 on the lateral surfaces of thedummy gate fill 260 and fin templates 151 can be removed by an etch backprocess that leaves the upper spacer liner 270 on the vertical surfacesof the inner protective cap 190.

FIG. 14 is a cross-sectional side view of an upper spacer liner on anupper portion of the inner protective cap after removal of the dummygate fill, in accordance with an embodiment of the present invention.

In one or more embodiments, the dummy gate fill 260 can be removed toexpose the inner protective cap 190 between the upper spacer liner 270and the top surface of the sacrificial spacer cap 255. The dummy gatefill 260 can be removed using an isotropic etch, for example, a wetetch, to ensure removal of dummy gate fill material below theoverhanging upper spacer liner 270.

In one or more embodiments, the exposed portion of the inner protectivecap 190 can be removed to expose the sidewalls of the vertical fin(s)131. The exposed portion of the inner protective cap 190 can be removedusing an isotropic etch selective for the material of the innerprotective cap. After removal of the exposed portion, an upper portionof the inner protective cap 190 can remain on the fin template 151,template liner 141, and at least a portion of the vertical fin 131. Aninner protective flange 192 can remain on the lower portion of thevertical fin 131 proximal to the bottom diffusion region 135 andsource/drain layer 230.

FIG. 15 is a cross-sectional side view of a protective cover layer andgate dielectric layer on the upper spacer liner and vertical fin, inaccordance with an embodiment of the present invention.

In one or more embodiments, a gate dielectric layer 280 can be formed onexposed portions of the sacrificial spacer cap(s) 255, vertical fin(s)131, inner protective cap 190, and upper spacer liner 270, where thegate dielectric layer 280 can be formed by a conformal deposition. Invarious embodiments, the gate dielectric layer 280 can be formed by ALD,PEALD, CVD, PECVD, or combinations thereof.

In one or more embodiments, the gate dielectric layer 280 can be aninsulating dielectric layer, for example, a silicon oxide (SiO), ahigh-K dielectric, or combinations thereof.

In various embodiments, an interfacial layer (IL) can be formed betweenat least a portion of the gate dielectric layer 280 and the vertical fin131, where the IL is in contact with the walls of the vertical fin(s)131, which can be a first interfacial layer, and a second layer incontact with the first layer can be the high-K dielectric, where thefirst interfacial layer can be silicon oxide (SiO) or an oxide of thevertical fin material. The oxide can be thermally or chemically formedon the vertical fin(s) 131. In various embodiments, the interfaciallayer can be formed by reacting the exposed portion of the verticalfin(s) 131 with an oxidizing agent that can produce a thin (e.g., 1 to 5monolayers) of oxide on the exposed portion of the vertical fin(s). TheIL can reduce the amount of interface trapped charge, D_(it), at thechannel-to-gate dielectric interface.

In various embodiments, the gate dielectric layer 280 can be a high-Kdielectric material that can include, but is not limited to, transitionmetal oxides such as hafnium oxide (e.g., HfO₂), hafnium silicon oxide(e.g., HfSiO₄), hafnium silicon oxynitride (Hf_(w)Si_(x)O_(y)N_(z)),lanthanum oxide (e.g., La₂O₃), lanthanum aluminum oxide (e.g., LaAlO₃),zirconium oxide (e.g., ZrO₂), zirconium silicon oxide (e.g., ZrSiO₄),zirconium silicon oxynitride (Zr_(w)Si_(x)O_(y)N_(z)), tantalum oxide(e.g., TaO₂, Ta₂O₅), titanium oxide (e.g., TiO₂), barium strontiumtitanium oxide (e.g., BaTiO₃—SrTiO₃), barium titanium oxide (e.g.,BaTiO₃), strontium titanium oxide (e.g., SrTiO₃), yttrium oxide (e.g.,Y₂O₃), aluminum oxide (e.g., Al₂O₃), lead scandium tantalum oxide(Pb(Sc_(x)Ta_(1-x))O₃), and lead zinc niobate (e.g.,PbZn_(1/3)Nb_(2/3)O₃). The high-k material can further include dopantssuch as lanthanum and/or aluminum. The stoichiometry of the high-Kcompounds can vary.

In one or more embodiments, a protective cover layer 290 can be formedon at least a portion of the gate dielectric layer 280, where theprotective cover layer 290 can be conformally deposited by ALD, PEALD,CVD, PECVD, or combinations thereof.

In one or more embodiments, the protective cover layer 290 can be ametal nitride that can be selectively etchable in relation to the gatedielectric layer 280, for example, titanium nitride (TiN), tantalumnitride (TaN), zirconium nitride (ZrN), niobium nitride (NbN), tungstennitride (WN), manganese nitride (MnN), or combinations thereof.

FIG. 16 is a cross-sectional side view of a temporary fill layer fillingthe spaces between the protective cover layer on the vertical fins, inaccordance with an embodiment of the present invention.

In one or more embodiments, a temporary fill layer 300 can be formed onthe protective cover layer 290, where the temporary fill layer 300 canbe blanket deposited on the protective cover layer 290, for example, byCVD, PECVD, or LPCVD. In various embodiments, the temporary fill layer300 can be an organic resist material or a low-k oxide material, forexample, PMMA, a carbon-doped silicon oxide, a porous silicon oxide, aspin-on silicon based polymeric material (e.g., tetraethylorthosilicatehydrogen (TEOS), silsesquioxane (HSQ) andmethylsilsesquioxane (MSQ)), or combinations thereof. The protectivecover layer 290 can be selectively etchable versus the temporary filllayer 300.

In various embodiments, the temporary fill layer 300 can extend abovethe top surface of the protective cover layer 290, and a CMP can be usedto remove the excess material and provide a smooth, flat surface.

FIG. 17 is a cross-sectional side view of a partially removed temporaryfill layer exposing a portion of the protective cover layer, inaccordance with an embodiment of the present invention.

In one or more embodiments, a portion of the temporary fill layer 300can be removed to expose a portion of the protective cover layer 290,where the temporary fill layer 300 can be removed by a selective etch.After removal, the top surface of the temporary fill layer 300 can be ator above the lower edge of the inner protective cap 190, so at least theportion of the gate dielectric layer 280 in contact with the verticalfin 131 is covered by the temporary fill layer 300. An upper portion ofthe protective cover layer 290 on the upper spacer liner 270 can beexposed after removal of the portion of the temporary fill layer 300.

FIG. 18 is a cross-sectional side view of an exposed upper spacer linerafter removal of a portion of the gate dielectric layer and protectivecover layer, in accordance with an embodiment of the present invention.

In one or more embodiments, the exposed portion of the protective coverlayer 290 can be removed from the underlying gate dielectric layer 280.The exposed portion of the gate dielectric layer 280 can then be removedto expose the underlying upper spacer liner 270. A portion of the gatedielectric layer 280 can remain on at least a portion of the verticalfin 131 where a gate structure can subsequently be formed. The remainingportion of the gate dielectric layer 280 can be covered by the remainingportion of the protective cover layer 290.

FIG. 19 is a cross-sectional side view of an exposed protective coverlayer after removal of the temporary fill layer, in accordance with anembodiment of the present invention.

In one or more embodiments, the temporary fill layer 300 can be removedto expose the underlying protective cover layer 290. The temporary filllayer 300 can be removed by a selective isotropic etch to remove theportion of the temporary fill layer 300 that can be in the recess formedby the protective cover layer 290 and gate dielectric layer 280.

In one or more embodiments, the lip formed by the protective cover layer290 and gate dielectric layer 280 protruding perpendicularly away fromthe vertical fin sidewall can be selectively removed with an isotropicwet etch.

FIG. 20 is a cross-sectional side view of a work function layer on theupper spacer liner and gate dielectric layer, in accordance with anembodiment of the present invention.

In one or more embodiments, the protective cover layer 290 can beremoved to expose the underlying gate dielectric layer 280 on one ormore vertical fin(s) 131, where the protective cover layer 290 can beremoved using a selective isotropic wet etch.

In one or more embodiments, a work function layer 310 can be formed onthe exposed portions of the gate dielectric layer 280, upper spacerliner 270, and top surfaces of the fin template(s) 151 and innerprotective cap 190. The work function layer 310 can be formed by aconformal deposition, for example, ALD, PEALD, CVD, PECVD, andcombinations thereof.

In one or more embodiments, a work function layer 310 can be formed onthe gate dielectric layer 280 exposed by removal of the protective coverlayer 290. The work function layer 310 can be formed on the gatedielectric layer 280 to adjust the electrical properties of a gateelectrode. In various embodiments, the work function layer 310 can beoptional.

In various embodiments, a work function layer 310 can be a conductivenitride, including but not limited to titanium nitride (TiN), titaniumaluminum nitride (TiAlN), hafnium nitride (HfN), hafnium silicon nitride(HfSiN), tantalum nitride (TaN), tantalum silicon nitride (TaSiN),tungsten nitride (WN), molybdenum nitride (MoN), niobium nitride (NbN);a conductive carbide, including but not limited to titanium carbide(TiC), titanium aluminum carbide (TiAlC), tantalum carbide (TaC),hafnium carbide (HfC); or combinations thereof. The work function layer310 may include multiple layers of work function materials, for example,a work function layer 310 can be a TiN/TiC stack.

In various embodiments, the work function layer 310 can have a thicknessin the range of about 3 nm to about 11 nm, or can have a thickness inthe range of about 5 nm to about 8 nm.

FIG. 21 is a cross-sectional side view of a gate metal fill on the workfunction layer, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a gate metal fill 320 can be formed on atleast a portion of the work function layer 310. The gate metal fill 320can be formed by a blanket deposition, where the gate metal fill 320 canextend above the top surfaces of the work function layer 310 on the fintemplates 151. The gate metal fill 320 can fill in the space(s) betweenthe vertical fins 131. A CMP can be used to reduce the height of thegate metal fill 320.

In various embodiments, the gate metal fill 320 can be a conductivemetal, where the metal can be tungsten (W), titanium (Ti), molybdenum(Mo), cobalt (Co), or a conductive carbon material (e.g., carbonnanotube, graphene, etc.), or any suitable combinations thereof.

FIG. 22 is a cross-sectional side view of a reduced height gate metalfill on the work function layer, in accordance with an embodiment of thepresent invention.

In one or more embodiments, an exposed portion of the gate metal fill320 can be removed to reduce the height of the gate metal fill 320.Removal of a portion of the gate metal fill 320 can expose a portion ofthe work function layer 310.

In one or more embodiments, a portion of the work function layer 310exposed by the reduction in height of the gate metal fill 320 can beremoved, where the exposed portion of the work function layer 310 can beremoved by a selective isotropic wet etch. The top surfaces of the gatemetal fill 320 and the work function layer 310 can be above the level ofthe upper-most surface of the gate dielectric layer 280 and below thelevel of the top surface of the vertical fin(s) 131, where at least aportion of the work function layer 310 can remain on the upper spacerliner 270 after removal of the exposed portion of the work functionlayer 310.

In one or more embodiments, the gate metal fill 320, work function layer310, and gate dielectric layer 280 can form a gate structure on at leasta portion of one or more vertical fin(s) 131, where the gate metal fill320 and work function layer 310 can form a conductive gate electrode.

FIG. 23 is a cross-sectional side view of a recessed gate metal fill,work function layer, gate dielectric layer, and sacrificial spacer cap,in accordance with an embodiment of the present invention.

In one or more embodiments, a portion of the gate metal fill 320, workfunction layer 310, gate dielectric layer 280, and sacrificial spacercap 255 can be removed to reduce the lateral dimensions of the gatestructure and sacrificial spacer cap on one or more vertical fin(s) 131to form a recessed region 330. In various embodiments, the sacrificialbottom spacer 240 may not be partially removed by formation of therecess region(s) 330, such that at least a portion of the top surface ofthe sacrificial bottom spacer 240 can be exposed by formation of therecessed region(s) 330. The sacrificial bottom spacer 240 can act as anetch stop.

FIG. 24 is a cross-sectional side view of an inner liner on a recessedgate metal fill, work function layer, gate dielectric layer, andsacrificial spacer cap, in accordance with an embodiment of the presentinvention.

In one or more embodiments, the fin template(s) 151, template liners141, and a portion of the inner protective cap 190 and upper spacerliner 270 can be removed, where the fin template(s) 151, template liners141, and a portion of the inner protective cap 190 and upper spacerliner 270 can be removed by CMP. The CMP can provide a smooth, flatsurface at the top of the vertical fin(s) 131. In various embodiments, aportion of the vertical fin(s) 131 can also be removed, such that theheight of the vertical fin(s) 131 can be reduced by the CMP.

In one or more embodiments, an inner liner 340 can be formed on the topsurface of the vertical fin(s) 131, inner protective cap 190, upperspacer liner 270, and at least a portion of the sacrificial bottomspacer 240, where the inner liner 340 can be conformally deposited. Invarious embodiments, the inner liner 340 can be silicon oxide (SiO) orsilicon oxynitride (SiON), where the inner liner 340 can be selectivelyremoved in relation to the inner protective cap 190, upper spacer liner270, and sacrificial bottom spacer 240.

FIG. 25 is a cross-sectional side view of a sacrificial top spacer fillon the inner liner over the vertical fins and gate structures, inaccordance with an embodiment of the present invention.

In one or more embodiments, a sacrificial top spacer fill 350 can beformed on the inner liner 340, where the sacrificial top spacer fill 350can be blanket deposited on the inner liner 340 over the vertical fins131 and gate structures.

In one or more embodiments, the sacrificial top spacer fill 350 can bean easily selectively etchable material, for example, silicon nitride(SiN), amorphous carbon (a-C), amorphous silicon (a-Si),silicon-germanium (SiGe), or suitable combinations thereof.

FIG. 26 is a cross-sectional side view of a reduced height sacrificialtop spacer fill on the inner liner after partial removal, in accordancewith an embodiment of the present invention.

In one or more embodiments, the sacrificial top spacer fill 350 can bepartially removed to expose the top surfaces of the vertical fin(s) 131,inner protective cap 190, and upper spacer liner 270. A portion of theinner liner 340 can be exposed by removal of the portion of thesacrificial top spacer fill 350. The sacrificial top spacer fill 350 canbe partially removed by chemical-mechanical polishing (CMP) to provide asmooth flat surface, while leaving a portion of the sacrificial topspacer fill 350 in U-shaped trough(s) 345 formed by the inner liner 340between adjacent upper spacer liners 270.

FIG. 27 is a cross-sectional side view of a top source/drain region onthe top surfaces of the vertical fins and sacrificial top spacer fill,in accordance with an embodiment of the present invention.

In one or more embodiments, a top source/drain 360 can be formed on theexposed top surfaces of the vertical fins 131 and sacrificial top spacerfill 350 in the U-shaped trough(s) 345. The top source/drain 360 can beformed by epitaxially growing source/drain region(s) on one or morevertical fin(s) 131. In various embodiments, the source/drain region(s)can be grown on two or more adjacent vertical fins 131 until thesource/drain regions coalesce into a merged top source/drain 360 thatspans two or more vertical fins 131 and covers at least one U-shapedtrough 345 with a sacrificial top spacer fill 350 in the trough bed.

FIG. 28 is a cross-sectional side view of dopant diffusion into an upperportion of the vertical fins utilizing a heat treatment, in accordancewith an embodiment of the present invention.

In one or more embodiments, the vertical fin(s) 131 and top source/drain360 can be heat treated to facilitate diffusion of dopant from the topsource/drain 360 into the adjacent vertical fin(s) 131. In variousembodiments, the top source/drain 360 and vertical fin(s) 131 can beheat treated at a temperature in the range of about 700° C. to about1300° C., or in the range of about 900° C. to about 1100° C., where theheat treatment can be a furnace anneal, a rapid thermal anneal, or alaser anneal. In various embodiments the anneal can be for a duration inthe range of about 5 seconds to about 1 hour, where the duration of theheat treatment can depend upon the temperature.

In various embodiments, the top source/drain 360 can have a dopantconcentration in the range of about 1×10¹⁹ to about 1×10²¹, or in therange of about 5×10¹⁹ to about 5×10²⁰. The top diffusion region 137 inthe upper portion of the vertical fin(s) 131 can have a dopantconcentration in the range of about 1×10¹⁸ to about 1×10²⁰, or in therange of about 5×10¹⁸ to about 5×10¹⁹, after the heat treatment.

FIG. 29 is a cross-sectional side view of a top source/drain on thevertical fins after removal of the exposed portion of the sacrificialtop spacer fill, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a portion of the sacrificial top spacer fill350 not covered by the top source/drain 360 can be removed to expose aportion of the inner liner 340, whereas the portion(s) of thesacrificial top spacer fill 350 in the U-shaped trough 345 can remain.

FIG. 30 is a layered top view of a fin layout showing an arrangement ofhidden features, in accordance with an embodiment of the presentinvention.

In various embodiments, a vertical finFET device can be laid out on aburied oxide layer 120, where the surface of the BOX layer can extendlaterally beyond the formed features of the device. A source/drain layer230 (shown as a dotted line) formed on the buried oxide layer 120 canextend laterally outward away from the vertical fin(s) 131 (shown assolid lines) and gate metal fill 320 (shown as a double solid line), soan electrical contact can be formed past the higher device layers to thesource/drain layer 230 without interference or shorting to other devicecomponents. The gate metal fill 320 can extend laterally past one end ofthe vertical fin(s) 131, and sacrificial top spacer fill 350, so anelectrical contact can be formed past these device layers. Sacrificialbottom spacer(s) 240 (shown as long dashed lines) can be on thesource/drain layer 230, and below the gate metal fill 320.

The sacrificial top spacer fill 350 (shown as solid lines) can be abovethe gate metal fill 320, and smaller laterally than the sacrificialbottom spacer(s) 240 by approximately the sidewall width of the U-shapedtrough 345 (not shown). The sacrificial top spacer fill 350 can belonger than the vertical fin(s) 131 in at least one direction, such thata vertical opening can be made to the sacrificial top spacer fill 350without exposing an endwall of the vertical fin(s). The vertical fin(s)131 can also be surrounded by an inner protective liner 190 and upperspacer liner 270 (shown together as a short dashed line around thevertical fin(s) 131).

The inner liner 340 can cover the sacrificial bottom spacer(s) 240, gatemetal fill 320, and a portion of the endwalls of the vertical fin(s)131, while leaving the sacrificial top spacer fill 350 uncovered. Theinner liner 340 can protect the covered device components and layersduring formation of a vertical opening and etching of the sacrificialtop spacer fill 350.

FIG. 31 is a cross-sectional side view of an interlayer dielectric layeron the top source/drain and previously exposed inner liner, inaccordance with an embodiment of the present invention.

In one or more embodiments, an interlayer dielectric (ILD) layer 370 canbe formed on the top source/drain(s) 360 and on the portions of theinner liner 340 exposed by removal of the sacrificial top spacer fill350.

In one or more embodiments, the interlayer dielectric layer 370 can be asilicon oxide (SiO) or a low-k dielectric material. In variousembodiments, a low-k dielectric material can be a fluoride-doped siliconoxide (e.g., fluoride doped glass), a carbon-doped silicon oxide, aporous silicon oxide, a spin-on silicon based polymeric material (e.g.,tetraethyl orthosilicatehydrogen (TEOS), silsesquioxane (HSQ) andmethylsilsesquioxane (MSQ)), or combinations thereof.

In various embodiments, the ILD layer 370 can be blanket deposited onthe top source/drain 360. In various embodiments, the ILD layer 370 canbe formed by CVD, LPCVD, or spun on.

FIG. 32 is a cross-sectional top view of FIG. 31 along the AA sectionshowing a plurality of vertical fins and intervening sacrificial topspacer fill in the U-shaped troughs with an opening in the ILD layer, inaccordance with an embodiment of the present invention.

In one or more embodiments, an opening 400 can be formed in the ILDlayer 370, where the opening extends from the top surface of the ILDlayer 370 to a depth that exposes at least a portion of the sacrificialtop spacer fill 350 at one end of the vertical fins 131. Differentopenings 400 can be formed to different U-shaped troughs 345.

FIG. 33 is a cross-sectional side view of upper void spaces formed inthe U-shaped troughs after removal of the sacrificial top spacer fill,in accordance with an embodiment of the present invention.

In one or more embodiments, an isotropic etchant selective for thematerial of the sacrificial top spacer fill material can be introducedinto the opening 400 formed in the ILD layer 370, such that thesacrificial top spacer fill 350 can be selectively removed from withinthe U-shaped troughs 345 to form upper void space(s) 355, which can beair gaps between a top source/drain 360 and a gate structure in a finFETdevice.

FIG. 34 is a cross-sectional top view of FIG. 33 along the same AAsection as FIG. 31 showing a plurality of vertical fins and upper voidspaces in the U-shaped troughs, in accordance with an embodiment of thepresent invention.

In one or more embodiments, the upper void space(s) 355 can extend alongthe full length of the U-shaped troughs 345 from one end of the verticalfin 131 to the other end of the vertical fin. In various embodiments,the upper void space(s) 355 can extend along a portion of the length ofthe U-shaped troughs 345 from the end proximal to the opening in the ILDlayer at which the isotropic etchant is introduced to a point onlypartially along the length of the vertical fin 131. A portion of thesacrificial top spacer fill 350 can remain in the U-shaped troughs 345at the distal end from the opening in the ILD layer 370. Inner liner 340can cover components below the sacrificial top spacer fill.

In various embodiments, the opening 400 can be back-filled with an ILDmaterial, where the ILD back-fill can pinch off a portion of the voidspace(s) 355 (e.g., air gap) proximal to the opening 400.

FIG. 35 is a cross-sectional side view of bottom void spaces formed inthe U-shaped sacrificial spacer caps after removal of the sacrificialbottom spacer, in accordance with an embodiment of the presentinvention.

In one or more embodiments, an opening can be formed in the ILD layer370, where the opening extends from the top surface of the ILD layer 370to a depth that exposes at least a portion of the sacrificial bottomspacer 240 at one end of the vertical fins 131.

In one or more embodiments, an isotropic etchant selective for thematerial of the sacrificial bottom spacer 240 can be introduced into theopening formed in the ILD layer 370, such that the sacrificial bottomspacer 240 can be selectively removed from within the U-shapedsacrificial spacer cap 255 to form bottom void space(s) 245, which canbe air gaps between a source/drain layer 230 and a gate structure in afinFET device. The sacrificial spacer cap 255 can be on at least aportion of the source/drain layer 230 and in contact with at least aportion of the gate dielectric layer 280, wherein a sacrificial spacercap 255 bounds the bottom void space 245 on three sides and thesource/drain layer 230 bounds the bottom void space 245 on the fourthside.

In one or more embodiments, the bottom void space(s) 245 can extendalong the full length of the U-shaped sacrificial spacer cap 255 fromone end of the vertical fin 131 to the other end of the vertical fin. Invarious embodiments, the bottom void space(s) 245 can extend along aportion of the length of the U-shaped sacrificial spacer cap 255 fromthe end proximal to the opening in the ILD layer 370 at which theisotropic etchant is introduced to a point only partially along thelength of the vertical fin 131. A portion of the sacrificial bottomspacer 240 can remain in the sacrificial spacer cap 255 at the distalend from the opening in the ILD layer 370, where removal can be a timedetch.

In various embodiments, separate openings in the ILD layer 370 can beused to introduced etchant to remove the sacrificial bottom spacer 240and the sacrificial top spacer fill 350. In various embodiments, opening400 can be used to introduce etchant to remove the sacrificial topspacer fill 350, whereas a second opening can be used to introduceetchant to remove the sacrificial bottom spacer 240.

FIG. 36 is a cross-sectional side view of enlarged bottom void spacesformed between the gate dielectric layer and source/drain layer afterremoval of the sacrificial spacer cap, in accordance with an embodimentof the present invention.

In one or more embodiments, the bottom void space(s) 245 can be enlargedby removing the sacrificial spacer cap(s) 255, where the sacrificialspacer cap(s) 255 can be removed by a selective etch introduced into anopening in the ILD layer 370. The enlarged bottom void space(s) 247 canbe bordered by the gate dielectric layer 280, the source/drain layer 230opposite the gate dielectric layer 280, and the inner protective flanges192 on the lower portion of the vertical fin 131. The gate dielectriclayer 280 can extend laterally between adjacent vertical fins 131 toform a cover over each of the enlarged bottom void space(s) 247, and theinner protective flanges 192 can form sidewalls around the enlargedbottom void space(s) 247. The sacrificial spacer cap(s) 255 can be adifferent material than the gate dielectric layer 280, the source/drainlayer 230, and the inner protective flanges 192, so the sacrificialspacer cap(s) 255 can be selectively removed.

FIG. 37 is a cross-sectional side view of further enlarged bottom voidspaces formed by partial removal of the source/drain layer, inaccordance with an embodiment of the present invention.

In one or more embodiments, a portion of the source/drain layer 230 canbe removed, where an etchant selective for the material of thesource/drain layer 230 can be introduced into the enlarged bottom voidspace(s) 247 to selectively etch the source/drain layer 230 to furtherenlarge the bottom void space(s) 247. The source/drain layer 230 can beetched using a hydroxide etchant to form angled faces along particularcrystal planes to increase the size of the void spaces 247, whilemaintaining an electrical connection along the source/drain layer 230 toeach vertical fin 131.

In a non-limiting exemplary embodiment, a potassium hydroxide solution(KOH) or ammonium hydroxide solution (NH₄OH) can be introduced into theenlarged bottom void space(s) 247, where the KOH preferentially etchessilicon <100> and <110> crystal planes compared to the <111> crystalplane, thereby forming facetted sides on the source/drain layer 230. Thefacetted sides can be at an angle to the vertical fin(s) 131 and notparallel to the plane of the substrate.

FIG. 38 is a cross-sectional side view of a silicide layer formed on thefaceted sides of the source/drain layer, and an opening in the ILDlayer, in accordance with an embodiment of the present invention.

In one or more embodiments, a gaseous reactant can be introduced intothe enlarged bottom void space(s) 247 to deposit a metal by ALD on theexposed faceted faces of the source/drain layer 230. In variousembodiments, the deposited metal can be a metal that can form a silicidelayer on the source/drain layer 230. In various embodiments, a heattreatment can be utilized to react the deposited metal with silicon ofthe source/drain layer 230 to form the silicide layer 238. Excess metalcan be removed from the surface of the silicide layer 238 by a selectiveetch.

In one or more embodiments, an opening 375 can be formed in the ILDlayer 370 above the top source/drain 360 for forming a subsequentelectrical contact to the top source/drain 360. In various embodiments,a portion of the top source/drain 360 can be removed by etching toreduce the thickness of the top source/drain 360.

FIG. 39 is a cross-sectional side view of a silicide layer formed on thetop source/drain layer, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a metal silicide layer 380 can be formed onthe top source/drain 360. A metal, including but not limited to Ni, Pt,NiPt, Co, etc., can be used to form the metal silicide layer 380, wherethe metal can be blanket deposited on the exposed surfaces and annealedat a suitable temperature to form the metal silicide layer. The metalcan be deposited, for example, by ALD, CVD, or a combination thereof.The unreacted metal can be removed by a selective etching.

FIG. 40 is a cross-sectional side view of an ILD refill formed in theopening above the top source/drain, in accordance with an embodiment ofthe present invention.

In one or more embodiments, the opening 375 above the top source/drain360 can be filled with an ILD material to cover the metal silicide layer380.

FIG. 41 is a cross-sectional side view of a second opening formed in theILD layer above the top source/drain layer, in accordance with anembodiment of the present invention.

In one or more embodiments, a second opening 377 can be formed in theILD refill down to the metal silicide layer 380 and top source/drain 360to form an electrical contact.

FIG. 42 is a cross-sectional side view of a conductive electricalcontact formed in the second opening formed in the ILD layer to thesilicide layer, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a conductive metal fill 390 can be formed inthe opening 377 to form a conductive electrical contact to the metalsilicide layer 380 and top source/drain 360. The conductive metal fill390 can be tungsten (W).

FIG. 43 is a top view of a multi-fin device showing the electricalcontacts to the various device components, in accordance with anembodiment of the present invention.

In one or more embodiments, a bottom source/drain contact 410 can beformed in an opening (e.g., via) in the ILD layer down to a portion ofthe source/drain layer 230. A top source/drain contact 420 can be formedin an opening in the ILD layer down to a portion of the top source/drain360. A gate contact 430 can be formed in an opening in the ILD layerdown to a portion of the gate metal fill 320. The top source/drain 360can have a top source/drain perimeter 369 the defines the lateralboundary of the top source/drain 360. The source/drain layer 230 canhave a source/drain layer perimeter 239 that defines the lateralboundary of the source/drain layer 230, where the source/drain layerperimeter 239 can be larger than the top source/drain perimeter 369. Thegate metal fill 320 can have a gate metal fill perimeter 329 thatextends beyond the top source/drain perimeter 369 in at least onedirection.

In one or more embodiments, a channel liner 402 can be formed in theopening 400, before the opening 400 is refilled with ILD material toseal the opening formed for etching the sacrificial top spacer fill 350.In various embodiments, the upper void space(s) 355 can extend beyondthe gate metal fill perimeter 329 and/or top source/drain perimeter 369on the sides of the finFET device.

In a non-limiting exemplary embodiments, a method of forming a multi-finfield effect transistor device with air gaps can include forming aplurality of fins on a substrate; forming a source/drain layer on thesubstrate between the plurality of fins on a substrate; forming asacrificial bottom spacer on the source/drain layer; forming asacrificial spacer cap on the sacrificial bottom spacer; forming a gatedielectric layer on at least a portion of the plurality of vertical finsand on the sacrificial spacer cap; and removing the sacrificial bottomspacer to form a bottom void space between the source/drain layer andthe gate dielectric layer.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

It should be understood that use of descriptions such as top, bottom,left, right, vertical, horizontal, or the like, are intended to be inreference to the orientation(s) illustrated in the figures, and areintended to be descriptive and to distinguish aspects of depictedfeatures without being limiting. Spatially relative terms, such as“beneath,” “below,” “lower,” “above,” “upper,” and the like, may be usedherein for ease of description to describe one element's or feature'srelationship to another element(s) or feature(s) as illustrated in theFIGs. It will be understood that the spatially relative terms areintended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the FIGs. Forexample, if the device in the FIGs. is turned over, elements describedas “below” or “beneath” other elements or features would then beoriented “above” the other elements or features. Thus, the term “below”can encompass both an orientation of above and below. The device may beotherwise oriented (rotated 90 degrees or at other orientations), andthe spatially relative descriptors used herein may be interpretedaccordingly. In addition, it will also be understood that when a layeris referred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Reference to first, second, third, etc.,feature is intended to distinguish features without necessarily implyinga particular order unless otherwise so stated or indicated. Thus, afirst element discussed herein could be termed a second element withoutdeparting from the scope of the present concept.

The present embodiments may include a design for an integrated circuitchip, which may be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer may transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present invention, as well as other variations thereof, means that aparticular feature, structure, characteristic, and so forth described inconnection with the embodiment is included in at least one embodiment ofthe present invention. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Having described preferred embodiments of a device and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. A method of forming a fin field effect transistordevice with air gaps, comprising: forming a vertical fin on a substrate;forming an inner protective cap on the vertical fin; forming an outerprotective cap on the inner protective cap; forming a source/drain layerin contact with the vertical fin; forming a sacrificial bottom spacer oneach side of the vertical fin, and on the source/drain layer; andforming a spacer cap layer on the sacrificial bottom spacer.
 2. Themethod of claim 1, wherein the substrate includes a buried oxide layer,and the source/drain layer is on the buried oxide layer.
 3. The methodof claim 1, wherein the spacer cap layer is the same material as theouter protective cap.
 4. The method of claim 3, further comprising,etching back the spacer cap layer and outer protective cap to form asacrificial spacer cap around the sacrificial bottom spacer.
 5. Themethod of claim 4, further comprising, forming a dummy gate fill on thesacrificial spacer cap on each side of the vertical fin.
 6. The methodof claim 5, further comprising, forming an upper spacer liner on anexposed portion of the inner protective cap.
 7. The method of claim 6,further comprising, removing the dummy gate fill to expose a portion ofthe vertical fin, and forming a gate structure on the exposed portion ofthe vertical fin.
 8. The method of claim 7, further comprising, formingan inner liner on the gate structure, and a sacrificial top spacer fillon the inner liner.
 9. The method of claim 8, further comprising,forming a top source/drain on the sacrificial top spacer fill andvertical fin, and removing at least a portion of the sacrificial topspacer fill and the sacrificial bottom spacer on each side of thevertical fin.
 10. A method of forming a fin field effect transistordevice with air gaps, comprising: forming one or more vertical fins on asubstrate; forming a source/drain layer on the substrate in contact withthe one or more vertical fins on a substrate; forming a sacrificialbottom spacer on the source/drain layer; forming a sacrificial spacercap on the sacrificial bottom spacer; and removing the sacrificialbottom spacer to form a bottom void space between the source/drain layerand the sacrificial spacer cap.
 11. The method of claim 10, wherein thesacrificial bottom spacer is silicon-germanium (Si_(x)Ge_(1-x)), siliconoxide (SiO), silicon oxycarbide (SiOC), silicon oxycarbonitride (SiOCN),amorphous carbon (a-C), or combinations thereof.
 12. The method of claim10, further comprising forming a gate dielectric layer on at least aportion of the one or more vertical fins and the sacrificial spacer cap.13. The method of claim 12, wherein the sacrificial top spacer fill issilicon nitride (SiN), amorphous carbon (a-C), amorphous silicon (a-Si),silicon-germanium (SiGe), or combinations thereof.
 14. The method ofclaim 13, further comprising forming a top source/drain on the one ormore vertical fins that spans the one or more vertical fins and covers aportion of the sacrificial top spacer fill.
 15. The method of claim 14,further comprising removing the sacrificial top spacer fill to form anupper void space, wherein the top source/drain bounds the upper voidspace on one side and the U-shaped trough bounds the upper void space onthree sides.
 16. The method of claim 15, wherein the sacrificial topspacer fill is removed using an isotropic wet etch.
 17. A method offorming a fin field effect transistor device with air gaps, comprising:forming a vertical fin on a substrate; forming an inner protective capon the vertical fin, wherein the inner protective cap is silicon oxide(SiO); forming an outer protective cap on the inner protective cap,wherein the outer protective cap is silicon nitride (SiN); forming asource/drain layer in contact with the vertical fin; forming asacrificial bottom spacer on each side of the vertical fin, and on thesource/drain layer, wherein the sacrificial bottom spacer issilicon-germanium (Si_(x)Ge_(1-x)); and forming a spacer cap layer onthe sacrificial bottom spacer, wherein the spacer cap layer is siliconnitride (SiN).
 18. The method of claim 17, wherein the silicon-germanium(Si_(x)Ge_(1-x)) has a germanium concentration of >50%.
 19. The methodof claim 17, further comprising, etching back the spacer cap layer andouter protective cap to form a sacrificial spacer cap around thesacrificial bottom spacer.
 20. The method of claim 19, furthercomprising, forming a dummy gate fill on the sacrificial spacer cap oneach side of the vertical fin.